Use of systems for controlling positioning of head assemblies relative to data tracks on recording media disks is well known. Typically, accurate head positioning is difficult to obtain. This is especially so with the advent of disks having higher track density.
It will be appreciated, therefore, that there is a need for a simple, inexpensive, yet reliable controller for precisely positioning a read/write head at preselected locations across data tracks on recording media.
However, many problems present themselves when attempting to achieve such goals. One is interchangeability, that is, data recorded on one drive system must be accurately read by another compatible disk drive system. Often this is difficult because of unintended manufacturing misalignments between different control systems. Given potential misalignment and interchangeability problems, as data density grows, accurate controlling of the head becomes even more essential and difficult.
For inexpensiveness and ease of operation in making and using controllers, it is desirable to use a simple reference signal which has linear characteristics. That is signal strength varies linearly with respect to distance along a sensing path. Typically, linear portions of such reference signals usually have a relatively short length. It is desirable, therefore, to extend the beneficial effects of such linearity in many control situations.
The present invention is intended to overcome the drawbacks mentioned above, as well as provide for improved control over transducer head positioning. Towards this end, the present invention contemplates method and apparatus for improving the control over positioning of a transducer assembly relative to data tracks on recording media.
Provision is made for apparatus which includes means movable about an axis and having mounted thereon a transducer assembly. Driving means is operable to move the movable means about the axis and thereby cause the transducer assembly to travel in overlying relationship across at least a portion of a band of data tracks. Provision is made for means for controlling the driving means and thereby effecting control over positioning of the transducer assembly to preselected positions across the width of the band. The controlling means includes sensing means which is mounted on one of the movable means or a member spaced from the movable means. Also included in the controlling means is means for providing a sensing reference control path. Such a control path has a preselected operational control length. The path is at a location which is at a predetermined ratio of the distance from the axis to the transducer assembly. In this manner, the effective controlled length of movement of the transducer assembly is increased relative to the preselected operational control length by an amount related to the noted ratio.
In an illustrated embodiment, the sensing means includes at least a pair of spaced apart magnetic sensing probes mounted on either the movable means or a member spaced from the movable means. The probes are at selected locations intermediate the axis and the transducer assembly. Magnetic means are provided for establishing a sensing reference path. The path has a preselected control length which is defined by a magnetic field having its strength vary along the extent thereof. The reference path is at a location along the movable means which is at a predetermined ratio of the distance between the axis and the head assembly. In this manner, the effect of the linearity of the control length is increased by an amount related to the ratio.
In such illustrated embodiment, the controlling means includes means operatively coupled to the probes for comparing the magnetic field strength sensed by the probes and determining the relative distance traversed by the head assembly as a function of each of the occurrences of one of the probes reading a value related to a stored value read of the other of the probes. Each occurrence is related to the incremental distance between the probes and thereby the extent of movement of the head assembly along the reference sensing path.
The present invention contemplates a method for achieving the noted transducer positioning.
Among the objects and features of the present invention are, therefore, the provision of an improved apparatus and method for controlling a transducer assembly relative to data tracks on a recording medium; the provision of an apparatus and method which increase the extent of control over positioning of the transducer assembly by a reference control signal having a finite linear length; the provision of an apparatus and method of the character last noted wherein the reference signal and signal sensing means are positioned intermediate a pivot axis for the transducer carrier and the transducer adjacent the distal end of such carrier; the provision of magnetic means for establishing the reference signal by a magnetic field having strength varying substantially linearly along the extent thereof; and the provision of a signal sensing means employing at least a pair of field probes which compare the strength read by one probe against the stored value of a second probe wherein each occurrence of a stored value being read by the one probe indicates traversal of a distance of the transducer which is related to the distance between the probes and thereby the displacement of the transducer assembly.
Other objects and further scope of applicability of the invention will become apparent after reading a detailed description taken in conjunction with the accompanying drawing wherein like reference numerals indicate like structure throughout the several views.